1. Field of the Invention
The present invention relates to a composite thin-film magnetic head provided with an inductive write head element and a magnetoresistive effect (MR) read head element that has a current-perpendicular-to-plane (CPP) structure where a sense current flows in a direction perpendicular to surfaces of laminated layers, to a magnetic head assembly provide with the thin-film magnetic head, and to a magnetic disk drive apparatus provided with the magnetic head assembly.
2. Description of the Related Art
In order to satisfy the demand for higher recording density and downsizing in a hard disk drive (HDD) apparatus, higher sensitivity and larger output of a thin-film magnetic head are required. In accordance with the requirement, improvement in characteristics of a general giant magnetoresistive effect (GMR) head with a GMR read head element, which is currently manufactured, is now strenuously proceeding. Also, development of a tunnel magnetoresistive effect (TMR) head with a TMR read head element providing an MR change ratio twice or more as that of the GMR read head element is energetically performed.
Because of the difference in flowing directions of their sense currents, structures of these TMR head and general GMR head differ from each other. One head structure in which a sense current flows in a direction parallel with surfaces of laminated layers as in the general GMR head is called as a current-in-plane (CIP) structure, whereas the other head structure in which a sense current flows in a direction perpendicular to surfaces of laminated layers as in the TMR head is called as the CPP structure. In recent years, CPP-GMR heads not CIP-GMR heads are under development.
The CPP-structure head utilizes its magnetic shield layers themselves as electrodes. Therefore, in the CPP-structure head, a short-circuit between the magnetic shield layer and the MR layer that will be serious problems for the CIP-structure GMR head when narrowing its read gap essentially never occurs. Thus, the CPP-structure head is very effective for higher density recording.
Also, provided are CPP-GMR heads with spin valve magnetic multi-layered films including such as dual-spin valve type magnetic multi-layered films as well as in case of the CIP-GMR heads.
The more downsizing in the HDD apparatus with such magnetic read head element and magnetic write head element, however, causes a problem of crosstalk between a writing side and a reading side. Especially, more miniaturization of a magnetic head element causes an increase in density of a current flowing through the element due to a decrease in a cross section area of the element, as well as a decrease in heat dispersion. Moreover, higher frequency for writing results in a steep change in voltage applied to the write head element. Consequently, a crosstalk occurs from the writing side to the reading side.
A technique to reduce a crosstalk between trace conductors in the writing side and in the reading side is proposed in Klaas B. Klaassen et al., “Write-to-Read Coupling”, IEEE Trans. Magn. Vol. 38, pp 61-67, January 2002, which analyzes a coupling mechanism between the trace conductors formed on a suspension. In the description, it is concluded that almost all crosstalk is caused by the coupling between the trace conductors, not by the inner coupling in the magnetic head.
The inventors of this application analyzed and investigated the crosstalk between the writing and reading sides based upon the thought that the inner coupling must have a great influence on the crosstalk, as well as the coupling between the trace conductors.
As a consequence of the analyses and investigations, it has been revealed that there is a relationship between the generation of crosstalk and a parasitic capacitance between layers of a composite thin-film magnetic head provided with an inductive write head element and an MR read head element. Particularly, in the composite thin-film magnetic head provided with a CPP-structure read head element, because the lower and upper shield layers are used as electrodes and therefore a parasitic capacitance between the write coil and the upper shield layer certainly becomes larger than that between the write coil and the lower shield layer, a crosstalk voltage is produced across the read head element.
If the crosstalk voltage is produced in the CPP-GMR read head element, electro-migration will be advanced to invite a short-life of the read head element, and also mutual diffusion between the layers will be increased to deteriorate magnetic characteristics of the read head element. Whereas in the TMR read head element, if the crosstalk voltage is produced, pinholes may be formed in the barrier layer causing in dielectric breakdown and thus a great degradation of the reading characteristics due to a decrease in an electrical resistance of the element may be induced.
Furthermore, in the CPP-GMR read head element, noises broken into the substrate manifest at the lower shield layer side electrode that is near the substrate more than the upper shield layer side electrode, and thus the differences in noises between the lower shield layer side electrode and the upper shield layer side electrode are amplified by the preamplifier and are superimposed on the read out signal. Therefore, the CPP-GMR read head element is sensitive to external noises.
Under these circumstances, the assignee of this application proposed in U.S. patent application Ser. No. 11/205,072 filed on Aug. 17, 2005 a composite thin-film magnetic head provided with a CPP-structure MR read head element, which can reduce crosstalk between the read head element and a write head element and can be little affected by external noises. The proposed thin-film magnetic head is configured such that a parasitic capacitance C4 between a substrate and a lower shield layer of the read head element is substantially equal to a parasitic capacitance C2 between an upper shield layer of the read head element and a lower pole layer of the write head element, and that the lower pole layer has the same potential as the substrate.
In a composite thin-film magnetic head with such MR read head element and an inductive write head element, a distortion may be created at the MR read head element region due to heat produced by the inductive write head element. The interaction of this created distortion and a magnetic distortion of the magnetic material consisting of the read head element such as magnetic materials of a free layer, a pinned layer, a pin layer, a magnetic domain control layer, and upper and lower shield layers may deteriorate the MR read head element region. When the write current frequency increases, because the heating value increases, this problem becomes serious.
In order to prevent such problem from occurring, it is required to reduce transmission of the heat produced at the write head element to the read head element as much as possible. This reduction of the transmitting heat may be attained by increasing the distance between the lower magnetic pole layer of the write head element and the upper shield layer of the read head element or by increasing the thickness of the insulation layer there between, and/or by decreasing the distance between the lower shield layer of the read head element and the substrate or by decreasing the thickness of the insulation layer there between so as to dissipate the produced heat through the substrate.
In recent years, in order to solve problems that MR read head element and inductive write head element regions of a thin-film magnetic head are contracted due to a low environment temperature and thus a magnetic spacing that is an effective magnetic distance between these head elements and a surface of a magnetic disk increases causing reading and/or writing operations being impossible to perform, a heater is provided in each thin-film magnetic head to thermally expand these head element regions. For example, U.S. Pat. No. 5,991,113, US Patent publication No. 2003/0099054A1, US Patent publication No. 2003/0174430A1 and US Patent publication No. 2002/0191326A1 disclose such thin-film magnetic heads.
It is advantageous to form the heater at a position near the air bearing surface (ABS) side end surfaces of the MR read head element and the inductive write head element in order to enhance the thermal expansion efficiency of the heater. However, such arrangement of the heater will harm critical conditions in the manufacturing process of the MR read head element and the inductive write head element.
If the heater is formed between the lower magnetic pole layer of the inductive write head element and the upper shield layer of the MR read head element, it is possible to easily form the heater in the thin-film magnetic head without changing the critical conditions in the manufacturing process of the MR read head element and the inductive write head element.
If the distance between the lower magnetic pole layer of the write head element and the upper shield layer of the read head element is increased and also the distance between the lower shield layer of the read head element and the substrate is decreased as aforementioned to solve the problems due to the heating of the write head element, it becomes quite difficult to make the parasitic capacitances C2 and C4 equal to each other causing resistance performance of the magnetic head against the crosstalk voltage and against the external noises to deteriorate.
Furthermore, in the composite thin-film magnetic head with a CPP-structure MR read head element, if a heater is formed between the upper shield layer of the read head element and the lower magnetic pole layer of the write head element, a crosstalk between the heater and the MR read head element may be produced causing damage to the MR read head element.